1. Technical Field
The present invention relates generally to an apparatus and method for detecting an optical line fault in a Passive Optical Network (PON) and, more particularly, to an apparatus and method that are capable of detecting an optical line fault at the smart Remote Node (RN) of a PON.
2. Description of the Related Art
Due to mobile data traffic that has recently and explosively increased, attempts to implement wired/wireless networks as broadband networks, long-range networks, and highly-integrated networks have been actively conducted. In particular, in the field of a wired optical network, 1G Ethernet-PON (E-PON) technology and 2.5G Gigabit-PON (G-PON) technology have been commercialized and are now widely available in private homes. Further, it is expected that the standardization of 10G E-PON technology and 10 Gigabit-PON (XG-PON) technology will be completed and commercialized in the near future.
In this way, as optical network technology has rapidly evolved into broadband network technology, the strengthening of network maintenance functions for providing reliable services is necessarily required. From the standpoint of an optical layer, to improve the availability and reliability of networks, the occurrence of faults in an optical module and an optical line must be monitored in real time. Further, if faults have occurred, they must be detected within a short period of time and must be promptly recovered.
Generally, PON technology may be chiefly divided into time division multiplexing-PON (hereinafter referred to as “TDM-PON”) and wavelength division multiplexing-PON (hereinafter referred to as “WDM-PON”), based on a data multiplexing scheme. For respective PON technologies, the configurations and operation schemes of various optical line monitoring devices have been proposed.
One of schemes that are currently and widely used as systems for monitoring faults occurring in an optical link is a scheme using an Optical Time Domain Reflectometer (OTDR) system. Generally, this adopts a scheme in which an OTDR system is located at a central base station and monitoring light is transmitted to Optical Network Units (ONUs) using a wavelength differing from that of data used in an Optical Line Terminal (or Termination) (OLT), and in which the occurrence or non-occurrence of faults in distribution lines of the respective ONUs is determined based on the distribution waveforms of light components, reflected and received from the ONUs, on a time axis.
However, a line fault detection system using an OTDR system in the PON has several structural problems that need to be solved. First, a remote node is present in the PON structure, an Optical Power Splitter (OPS) is present in the TDM-PON, and an Arrayed Waveguide Grating (AWG) is present in the WDM-PON, thus functioning to distribute optical signals. In the case of OTDR monitoring light, there is a disadvantage in that it is very difficult to distinguish a reflected and returned optical signal from noise due to loss in a Remote Node (RN). As the length of an optical line has increased, such a phenomenon has become an increasing problem. Second, the PON structure is divided into feeder networks and distribution networks, but it is impossible to identify the distribution networks because monitoring light is summed in the case of ONUs present at the same distance. In order to solve this problem, there is a need to artificially set the distances of ONUs to different distances. However, this setting complicates the embedding and installation of distribution networks, thus increasing construction costs.
To date, various methods, such as a monitoring light encoding method and a wavelength variable OTDR, have been proposed to solve the above-described two problems, but they have low economic efficiency and low universality.
Therefore, an efficient optical layer management method and system are urgently required that are universally usable for TDM-PON and WDM-PON structures while solving the above-described two problems in the PON structure, that is, difficulty in the identification of monitoring light due to loss in a remote node and an optical line and the overlapping of OTDR signals caused by ONUs present at the same distance.
The background of a smart RN structure proposed in the present invention is given as follows: conventional technology is intended to simplify the operation and management of the network by configuring an RN using only passive elements if possible, but line management of an Optical Distribution Network (ODN) cannot be performed in real time due to the RN composed of only passive elements. Recently, for real-time management of an ODN, the use of active elements for ODN management is required in such a way as to use a Light Emitting Diode (LED) for indicating connection status on an optical distribution board and to use Radio Frequency Identification (RFID) and a Quick Response (QR) code for determining information of connections between optical fibers.
Consequently, the conventional technology is problematic in that it is difficult to distinguish a monitoring light signal from a noise signal due to loss occurring in an optical line and an RN, and it is also difficult to identify a distribution network due to the overlapping of monitoring light waveforms caused by ONUs present at the same distance.
As related preceding technology, Korean Patent Application Publication No. 2009-0100109 (entitled “Optical Fiber Monitoring Apparatus and Method Using Optical Pulse Pattern”) is disclosed. This patent discloses technology in which the pulse of reflected light measured at the optical cable of a subscriber-side optical network is compared with a previously measured normal state pulse to check the pulse pattern of the reflected light, and the state of a fault in the optical cable is inspected based on the pulse pattern of the reflected light, thus easily determining the fault state of the optical cable (e.g., occurrence or non-occurrence of a fault, a faulty cable, and a predicted faulty location).
As another related technology, Korean Patent Application Publication No. 2012-0030397 (entitled “Method and Apparatus for Fault Discovery in Passive Optical Network (PON)”) discloses technology for discovering a fault in an optical fiber in a PON.